1. Field of the Disclosure
The present disclosure relates to an image processing apparatus having a function of reading a captured image, a control method thereof, and an imaging apparatus.
2. Description of the Related Art
The optical axis and the center of the image sensor may be misaligned due to factors such as assembly error when assembling the imaging lens or attachment error when attaching the image sensor. Misalignment of this center position (hereinafter referred to as optical axis displacement) fluctuates in accordance with movement of the focal lens and the magnification lens. Japanese Patent Laid-Open No. 2007-60486 and Japanese Patent Laid-Open No. 2011-114794 disclose cameras that adjust the readout position of pixels on the image sensor so that the position on the optical axis at which an image of the object is formed does not move when the moveable lens group moves, such as during focus detection, zooming and the like.
In an imaging apparatus provided with a zoom (magnification) lens, such as Japanese Patent Laid-Open No. 2007-60486 and Japanese Patent Laid-Open No. 2011-114794, the following problems arise in the case where optical axis misalignment is corrected by changing the image read position according to the zoom position (magnification ratio).
To correct optical axis misalignment that differs depending on the zoom position, the image read position needs to be changed sequentially during the zoom operation. However, in the case of changing the read position sequentially during the zoom operation when the smallest unit of this read position is one pixel, the change in read position will be perceived by the user as instability on the screen or blurring on the screen, and appear unnatural. This problem can be suppressed by changing the read position in units sufficiently smaller than one pixel. In this case, the image of a read position corresponding to pixel positions having values of less than one pixel is generated by interpolating actual pixel values (of pixel positions that are an integer multiple of one pixel). For example, the pixel value corresponding to an intermediate position (1.5, 1) of the two pixels (x, y)=(1, 1) and (2, 1) adjacent in the x direction in an xy orthogonal coordinate system can be derived as the average value of the pixel value of (1, 1) and the pixel value of (2, 1). Note that this interpolation method is merely an example, and other interpolation methods may be used.
Thus, in the case of generating an image corresponding to the read position in units of less than one pixel by interpolation, the image of the read position corresponding to the zoom position at the time when the zoom operation stops may be an interpolated image. Since an interpolated image is an image constituted by pixel values estimated by interpolation, there is a problem in that sharpness decreases as compared with a clipped image that does not require interpolation.